Haven't used that combo exclusively but I've used both a X-T2 and a 100-400. I believe a Canon 7Dm2 with their excellent 100-400 will be a much better choice as it'll focus faster and more accurately on moving subjects. I was never really impressed with X-T2's continious autofocus but maybe I've been doing something wrong.

Also, that Canon combo costs probably the same brand new and you can save some money buy buying a used body.

If I were into birding, I'd seriously look into a Canon or Nikon first. 100-400 is a fine lens but it's more of a choice for you if you are already deep into Fuji X system. I don't think it'd be worth to switch to Fuji for that lens alone as pretty much every manufacturer offers something that is a better option in many ways.

The last firmware update did improve things a lot, yet not perfect. But as I expressed in the PL thread, the manual focus issue with the lens amongst other little bits is annoying and keeps the keeper rate below what I usually get with a DSLR.

But it brought up an idea in me: To get me a 100-400 Tamron or Sigma, latest generation, for my Nikon. I already had surprisingly good results with a borrowed Sigma and I wonder which will be the better package? For the 100-400 I've easier space in my bag than for the 150-600. And it's lighter, too.

I tried birds photography several times, some birds like seagulls are quite easy since they hover over your head and pass several times, for those even manual focus is easy, other birds are more challenging since all the time they give can be as little as 2-3 seconds.

Shooting seagulls with 7Dmkii is very easy, tracking works like a charm and is not fooled by some obstacles or even other birds passing by, however for other birds like European robins we have here that barely give you a second before disappearing between the branches of the trees, I barely have time framing, although I had some few acceptable shots, for those even with good tracking I hardly see a mirrorless camera cope with such speed.

There are some blue small birds I spot from time to time on the beach here, they are so quick I never managed framing one, let along shooting it